Thermoplastic vulcanizate compositions include blends of dynamically cured rubber and thermoplastic polymers. The rubber may be dispersed within the thermoplastic resin phase as finely-divided rubber particles. These compositions have advantageously demonstrated many of the properties of thermoset elastomers, yet they are processable as thermoplastics. Because thermoplastic vulcanizates are advantageously processable as thermoplastics, elastomeric articles are often extruded from thermoplastic vulcanizates using thermoplastic extruding techniques.
Thermoplastic vulcanizates have been modified with various additives. For example, extender oils have been included to improve manufacture, processing, and provide economic value to the compositions. Likewise, inert fillers, such as clays, have been added to facilitate manufacture and add economic value to the compositions. And, carbon black has been added as a colorant or as a UV protectant.
Advantageously, additives, such as oils and fillers, can be added to the thermoplastic vulcanizate during the manufacturing process prior to dynamic vulcanization. Moreover, the fact that thermoplastic vulcanizates are processable as thermoplastics allow for the inclusion of additives after dynamic vulcanization. That is, the additives, such as fillers and oils, can be blended into the molten thermoplastic vulcanizate composition after dynamic vulcanization. The ability to add constituents after vulcanization has been especially beneficial where the additives might interfere with the vulcanization process. For example, flame retardants, such as antimony trioxide and zinc borate hydrate, which could have an inverse impact on a phenolic cure system, have been added after dynamic vulcanization to thereby produce thermoplastic vulcanizates exhibiting flame resistance.
While thermoplastic vulcanizates have proven to be versatile by accommodating various additives that can enhance the manufacture, processability, and/or ultimate utility of the compositions, the addition of additives can have an adverse impact on the thermoplastic vulcanizates. For example, thermoplastic vulcanizates generally have limits on the level of filler materials or other particulates that can be incorporated into the composition without negatively impacting one or more characteristics of the manufacture, processability, or mechanical properties of the thermoplastic vulcanizate. For example, it has been observed that thermoplastic vulcanizate compositions that include large amounts of flame retardants have a tendency to plate out, which is a phenomenon where small amounts of flame retardant migrate to the surface of the composition and deposit on fabrication equipment such as molds. Given that thermoplastic vulcanizates are prepared by employing phase-inversion techniques to provide unique compositions wherein a cured rubber is dispersed throughout a continuous plastic matrix, the ability to predict whether particular additives or combinations of additives may have an adverse impact on the thermoplastic vulcanizates is often not feasible.
Current market demands seek elastomeric materials that exhibit UV resistance and ozone resistance, as well as flame resistance. For example, the market seeks elastomeric materials that meet the standards of UL94V2 and UL746CF1. There is a desire to meet these demands with thermoplastic vulcanizates. Commercially available thermoplastic vulcanizates cannot provide these properties. The present invention addresses this demand.